Despite the fact that mills for cross rolling have been developed comparatively long time ago, are widely used in the industry and their design is constantly improving, it has been impossible up to present time to eliminate the possibility of seizing a billet being rolled between shaping elements. The seizure of the workpiece may be caused by its insufficient preheating, incorrect selection of conditions of rolling or shaping tools etc. The amount of losses born by the enterprise in the given emergency situation depends on the fact how quickly the hot billet can be removed from the mill after the seizure. In this case the losses will be determined not only in terms of the working time during the downtime of the mill, but also by the cost of damaged shaping tools. Under the conditions of a long-time contact between the heated billet and the shaping tool, the metal of the latter is subjected to undesirable phase transformations (e.g. tempering). Also possible is the diffusion welding between the billet and the tool, thereby making the damage of the latter inevitable.
Known in the art are attempts to develop mills whose designed is provided with means for quickly eliminating an accident (GDR Pat. No. 584,80). In accordance with this patent, the mill comprises a non-detachable housing wherein are mounted for reciprocating motion parallel plates carrying a shaping tool. The plates are carried by for rollers whose eccentric shafts are fastened on the housing. In the case of a seizure it is sufficient to rotate the roller shafts following which the billet may be withdrawn. Thus, the mill can be loosened comparatively quickly which fact constitutes an obvious advantage of the described mill. However, the introduction of bearing rollers and eccentric shafts into the mill design has adversely affected the rigidity thereof. In the course of mill operation the eccentric shafts get bent under the action of great loads (up to 30 tons), thereby causing a change in the distance between deforming tools. Though the amount of deflection of the shafts is small, it can be sufficient for defective products to appear. For this reason, the above described mill can be employed for rolling only those billets which will be subsequently subjected to turning.
A mill for cross rolling disclosed in U.S. Pat. No. 4,016,738 (see also the advertising booklet "Stan poperechno-klinovoy prokatki", Physico-technical Institute of the Belorussian SSR Academy of Sciences, Minsk, "Nauka i tekhnika" Publishers, 1980) possesses a considerably higher rigidity. This mill comprises a detachable box-shaped housing having upper and lower portions. The upper portion is fastened on the lower one by a plurality of screws which are screwed into the lower portion of the housing. Inside the housing are disposed parallel plates of which one is mounted on guide members for reciprocating motion, while the other is rigidly fastened on the housing. On the plate surfaces facing each other there are fixed wedge-shaped deforming tools. The movable plate is coupled with a drive for moving the same. A comparatively high ridigity of such a mill is ensured by the fact that the plates are carried directly by the housing whose rigidity is considerably higher than that of the shafts in the above described analog. However, such an increase in the rigidity in the above described structure caused a certain degradation of such an important operating characteristic as maintenance suitability. In particular, in the case of the mill seizure about 50 screws are to be unscrewed to release the upper plate and to withdraw the billet. It is obvious that such an operation requires a considerable time during which the hot billet may locally increase the temperature of deforming tools up to a dangerous limit (e.g. up to a temperature of the beginning of phase transformations in the tool metal). It is to be noted that the attempts to eliminate this disadvantage by decreasing the number of screws turned out to be unsuccessful since they resulted in a considerable decrease in the mill rigidity.